A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries, such as those located within the coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.
For example, stent prostheses have been previously disclosed for implantation within body lumens. Various stent designs have been previously disclosed for providing artificial radial support to the wall tissue, which forms the various lumens within the body, and often more specifically within the blood vessels of the body.
Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty,” “PTA” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. In some instances the vessel restenoses chronically, or closes down acutely, negating the positive effects of the angioplasty procedure.
To provide radial support to the treated vessel in order to prolong the positive effects of PTCA, a stent may be implanted in conjunction with the procedure. Effectively, the stent overcomes the natural tendency of the vessel walls of some patients to close back down, thereby maintaining a more normal flow of blood through that vessel than would be possible if the stent were not in place. Under this procedure, the stent may be collapsed to an insertion diameter and inserted into a body lumen at a site remote from the diseased vessel. The stent may then be delivered to the desired site of treatment within the affected lumen and deployed to its desired diameter for treatment.
Access to a treatment site is most often reached from the femoral artery. A flexible guiding catheter is inserted through a sheath into the femoral artery. The guiding catheter is advanced through the femoral artery into the iliac artery and into the ascending aorta. Further advancement of the flexible catheter involves the negotiation of an approximately 180 degree turn through the aortic arch to allow the guiding catheter to descend into the aortic cusp where entry may be gained to either the left or the right coronary artery, as desired. Because the procedure requires insertion of the stent at a site remote from the site of treatment, the device must be guided through the potentially tortuous conduit of the body lumen to the treatment site. Therefore, the stent must be capable of being reduced to a small insertion diameter and must be flexible.
An example of a stent that displays high radial strength includes, but is not limited to, the undulating stent disclosed in U.S. Pat. No. 5,292,331 to Boneau, the disclosure of which is herein incorporated by reference. Other examples of undulating stents include but are not limited to those disclosed in U.S. Pat. No. 4,580,568 issued to Gianturco, U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 5,195,984 issued to Schatz, or U.S. Pat. No. 5,514,154 issued to Lau. For example, the Gianturco stent generally has long undulations, while the Schatz and Lau stents generally have smaller undulations. However, in each case, these designs have undulations of the same length.
Once an undulating stent is positioned across the lesion, it is expanded. As it expands, straight portions of undulations, or segments, move apart, such that the segment, turn, segment angle increases. As the angle increases, the length of the overall stent tube contracts and the diameter expands. This foreshortening of the longitudinal length of the stent makes it difficult to ensure that a particular undulating stent will be long enough to cover the lesion effectively when expanded.
Further, various characteristics become important when the stent is expanding to a small diameter versus when it is expanded to a larger diameter. For instance, a stent designed for use in a larger vessel would likely have insufficient radial strength at a smaller diameter. Similarly, a stent designed for use is smaller vessels would suffer from excessive foreshortening, bunching and reduced scaffolding if used at a larger diameter.
Thus, it is desirable to have an interlumenal stent device, which provides improved radial strength, scaffolding and flexibility, without foreshortening or bunching when expanded to a variety of larger and smaller diameters.